Stabilization of polyvinyl chloride resins

ABSTRACT

A POLYVINYL CHLORIDE RESIN STABILIZER COMBINATION HAVING A READILY CONTROLLED TIN CONTENT IS PROVIDED WHICH LESSENS THE DEVELOPMENT OF EARLY DISCOLORATION OF THE RESIN WHEN HEATED AT ELEVATED TEMPERATURES, FOR EXAMPLE, 350*F., COMPRISING A DIORGANOTIN MERCAPTOCARBOXYLIC ACID ESTER AND A DIORGANOTIN OXIDE-ESTER COMPLEX WHICH IS A REACTION PRODUCT OF A DIORGANOTIN OXIDE AND AN ESTER OF AN OXYGEN-CONTAINING ACID. THE ABOVE STABILIZER COMPONENTS CAN BE LIQUIDS OR SOLIDS. HOWEVER, WHERE THE STABILIZER COMPONENTS ARE LIQUID, A HOMOGENEOUS STABLE LIQUID MIXTURE IS FORMED. POLYVINYL CHLORIDE RESIN COMPOSITIONS AND A PROCESS FOR STABILIZING SUCH RESINS ARE ALSO PROVIDED, USING THE ABOVE STABILIZER COMBINATION, THE RESINS HAVING AS A RESULT INCREASED RESISTANCE TO THE DEVELOPMENT OF EARLY DISCOLORATION WHEN HEATED AT ELEVATED TEMPERATURES. A PROCESS ALSO IS PROVIDED FOR PREPARING ORGANOTIN STABILIZER COMPOSITIONS HAVING A LOW TO HIGH TIN CONTENT CONTROLLABLE OVER A WIDE RANGE WITHOUT LIMITATIONS DUE TO STOICHIOMETRIC CONSIDERATIONS.

Feb' 8 1972 1 R. BRECKER EVAL 3,40595 STABILIZATION OF POLYVINYL GHLORIDE RESINS Filed Jan. 25, 1969 Paris per/ IOO ports resin United States Patent 3,640,953 STABILIZATION OF POLYVINYL CHLORIDE RESINS Lawrence R. Brecker, Brooklyn, and Alfred Thee, Long Beach, N.Y., assignors to Argus Chemical Corporation, Brooklyn, N.Y.

Filed Jan. 23, 1959, Ser. No. 793,503 Int. Cl. C081. 4.5/62

U.S. Cl. 260-45.75 K 24 Claims ABSTRACT F THE DISCLOSURE A polyvinyl chloride resin stabilizer combination having a readily controlled tin content is provided which lessens the development of early discoloration of the resin when heated at elevated temperatures, for example, 350 F., comprising a diorganotin mercaptocarboxylic acid ester and a diorganotin oxide-ester complex which is a reaction product of a diorganotin oxide and an ester of an oxygen-containing acid. The above stabilizer components can be liquids or solids. However, where the stabilizer components are liquid, a homogeneous stable liquid mixture is formed.

Polyvinyl chloride resin compositions and a process for stabilizing such resins are also provided, using the above stabilizer combination, the resins having as a result increased resistance to the development of early discoloration when heated at elevated temperatures.

A process also is provided for preparing organotin stabilizer compositions having a low to high tin content controllable over a wide range without limitations due to stoichiometric considerations.

SPECIFICATION This invention relates to polyvinyl chloride resin stabilizer compositions having a controlled tin content, and comprising a diorganotin mercaptocarboxylic acid ester and a diorganotin oxide complex with an ester of an oxygen-containing acid, and optionally, a stannous tin salt; to polyvinyl chloride resin compositions containing such stabilizer compositions and having as a result an improved resistance to the development of early discoloration during heating at elevated temperatures; to a process for improving the resistance of polyvinyl chloride resins to development of early discoloration, when heated at elevated temperatures, using such compositions; and to a process for preparing organotin stabilizers having a tin content readily controllable over a wide range without limitations due to stoichiometric considerations.

BACKGROUND AND PRIOR ART The stabilizing effectiveness of organotin stabilizers for polyvinyl chloride resins is generally associated with the type of organotin group, tin content, and the anion linked to the organotin group. In the development of the organotin stabilizer the aim has always been to nd the proper balance of these factors and combine them, preferably in a single compound.

Thus, for example, organotin oxides and suldes were suggested in U.S. Pat. No. 2,267,777 to Yngve, U.S. Pat. No. 2,746,946 to Weinberg and U.S. Pat, No. 3,021,302 to Frey as stabilizers for polyvinyl chloride. These products oier the highest possible tin and sulfur anion content (which are considered the active components) per molecule. However, these materials are not very etiective stabilizers and have never achieved any commercial success. With regard to these materials, it must, of course, be kept in mind that the organotin oxide have only a ice superficial similarity to the organotin sulfide, and are really very different, both physically and in their stabilizing effectiveness. The sullides are generally liquids, and the oxides are solids; the oxides have no odor, and are generally incompatible with polyvinyl chloride resin compositions, and particularly with other liquid additives for the resins, whereas sulfides have a very unpleasant odor but are compatible. Thus, these compounds are not really equivalent, although they are mentioned together in the patent literature.

U.S. Pats. Nos. 2,597,920 to Carroll dated May 27, 1952 and 2,763,632 to Johnson dated Sept. 18, 1956 disclose reaction products of diorganotin oxides and esters of oxygen-containing acids, such as ethyl acetate and butyl butyrate, as heat and light stabilizers for vinyl chloride resins. However, these reaction products are also rather poor in stabilizing effectiveness, ydespite their relatively high tin content, and are incapable of meeting modern standards for stabilizers.

Other disclosures of polymeric organotin compounds, which geneally include a chain of tin atoms connected through oxygen or sulfur atoms, are set out in U.S. Pats. Nos. 2,626,953, dated Jan. 27, 1953; 2,628,211, dated Feb. 10, 1953; 2,938,013, dated May 24, 1960 and 3,184,430, dated May 18, 1965. However, none of these organotin compounds is eiective enough to meet the requirements of present day stabilizers.

Of all the organotin compounds disclosed in the literature, the organotin mercaptides have been recognized as providing the most effective stabilization, and within this general group of organotin compounds, the organotin mercaptoacid esters have become most prominent, and are now recognized as being the most effective stabilizers for inhibiting the degradation of polyvinyl chlorides resins at high temperatures; e.g., 350 F. or 375 F., to which they are subjected during processing. This specific class of organotin stabilizers has been described in U.S. Pats. No. 2,641,588 and 2,641,596 to Leistner et al., U.S. Pat. No. 2,648,650 to Weinberg et al., and U.S. Pat. No. 2,809,956 to Mack et al. Furthermore, even within this limited class of organotin mercapto esters, only one type in particular has achieved outstanding commercial success, and that is the dialkyltin bis-alkyl thioglycolates. The ydialkyltin bis-alkyl thioglycolate esters have set the standards in the art, and the efforts of the industry have been directed to match or to improve on this particular type.

The search for even better stabilizers is primarily motivated because of certain drawbacks of the dialkyltin bisalkyl thioglycolates. First of all, they are mercaptides, and thus produce an objectionable odor during the processing of resins at elevated temperatures, and the resins often retain some of this odor in the finished article. A further drawback is their adverse effect on light stability which is also caused by the mercapto group. Another drawback is their inability to completely prevent early discoloration, that is, the yellowing which develops during the first 15 to 30 minutes of heating, particularly in clear rigid formulations.

Although early discoloration is not nearly so intense as later discoloration and embrittlement, arising from heat deterioration of the resin, it has been recognized that the early discoloration arising during the first 15 to 30 minutes of heating affects a relatively greater proportion of the resin. This is because the average period of time during which a given amount of resin product remains in the processing equipment, even in a continuous process which includes recycling of portions of the worked product, is less than thirty minutes. Only a minor portion of the resin will be subjected to Working temperatures for periods of up to one hour or longer. Hence, the preservation of a good color during the rst thirty minutes of heating can be more important than the protection of the relatively smaller proportion of the resin by long term heat staabilizers, such as the organotin mercapto acid esters.

A non-organotin stalbilizer combination capable of minimizing initial color and retaining good long term stability is disclosed in U.S. Pat. No. 2,997,454, patented Aug. 22, 1961, to Leistner et al., based on heavy metal salts of a higher fatty acid, and organic triphosphites, or such phosphites and polyvalent metal salts of hydrocarbon-substituted phenols, combined with an acid phosphorus compound having at least one acidic hydrogen atom attached through oxygen to phosphorus. This type of compound is not useful with organotin compounds to minimize early discoloration.

A number of patents have been directed to improving organotin-based stabilizers. For example, U.S. Pat. No. 2,914,506 to Mack et al., dated Nov. 24, 1959, suggests combinations of organotin thioglycolates with metallic and non-metallic stabilizers, including metal salts, epoxy compounds, phosphites and phenols. U.S. Pat. No. 2,938,013 to Mack et al., dated May 24, 1960, discloses combinations of organotin half ester maleates with other organotin compounds, metal salts, phosphites and epoxy compounds. Lazcano British Pat. 1No. 1,008,589, published Oct. 27, 1965, discloses combinations of organotin half ester maleates and thioglycolates with other metal salts, phenols, epoxy compounds, phosphites and polyols. None of these combinations is effective in significantly minimizing early discoloration.

British Pat. No. 874,574 to Luz, published Aug. 10, 1961, describes stabilizer compositions composed of organotin salts of cariboxylic acids, such as dibutyl tin diacetate and free thioglycolic acid esters. These compositions are not any better, from the standpoint of early discoloration, than the organotin mercapto acid ester salts. British Pat. No. 771,857 published Apr. 3, 1957, discloses combinations of mercapto acid esters in a large excess with organotin oxides.

Wooten et al., U.S. Pat. No. 3,063,963, issued Nov. 13, 1962, disclose combinations of organotin carboxylates of monoor dicarboxylic acids with omega mercapto acids or mercapto alcohols to improve weathering resistance of polyvinyl chloride resins.

More recently, U.S. Pat. No. 3,396,185 to Heckenbleikner et al. discloses specific types of polymeric monoalkyltin compounds. However, mono-alkyltin compounds, although known for a long time, have not found much success as polyvinyl chloride stabilizers, compared to the dialkyltin derivatives.

French Pat. No. 1,472,990 to Albright and Wilson discloses organotin mercaptides having at least one halogen attached to the tin atom. These compounds when used as polyvinyl chloride stabilizers prevent early discoloration of the polyvinyl chloride resin on heating, but shorten considerably the long-term stability, and therefore have very limited utility. In any event, these materials are still not comparable to the well-known simple dialkyltin mercapto acid esters.

Netherlands patent publication No. 6707180 to Deutsche Advance teaches combinations of conventional Well known dialkyltin mercaptides with the polymeric organotin compounds of Heckenlbleikner (US. Pat. No. 3,396,185, discussed above), which involves combining monoalkyltin and dialkyltin compounds.

Canadian Pat. No. 794,373 dated Sept. 10, 1968, describes novel organotin stabilizers derived from the reaction of organotin oxides or suldes or hydrocarbyl tin stannonic or thio stannonic acids or esters with organotin salts of mercapto monocarboxylic acid esters. These new organotin mercapto acid ester compounds have the formula RnSnZ4-n 4 where R is a monovalent organic group, generally an alkyl group, n is an integer from 1 to 3, and Z has the formula wherein R is the monovalent radical of an alcohol used to esterify the carboxyl group of the mercapto acid and generally is an alkyl group having not more than 20 carbon atoms, A is phenylene or an alkylene chain of at least two methylene groups, which may be interrupted by phenylene, B is RRSnO, RRSnS, RSnOOH, RSnSSH, RSnOOR" or RSnSSR, wherein R and R" are as dened above. However, these compounds do not avoid the stoichiometric limitations, because of the limits imposed by this formula. It is necessary to form the reaction products, it is explained, because organotin oxides and organotin suldes are incompatible with organotin mercapto acid esters, and with polyvinyl chloride resins. The structural relationship, i.e., the position of the mercapto group relative to the carboxyl group, is very critical. A (which may include a phenylene group) must have at least two carbon atoms intervening |between the -S- and COOR groups. `Esters of suitable acids are the esters of mercaptopropionic acid, ,B- to w-mercapto lauric acids, mercaptophenyl acetic acid and mercaptobenzoic acid. This class of tin compounds suiers from the inherent limitation that the Ja-mercaptoacid esters are excluded. Esters of thioglycolic acid will not react with the excess dialkyltin oxide to form the novel stabilizers, and these esters happen to be the least expensive and most readily available.

In addition to the problem of imparting early discoloration to polyvinyl chloride resins, organotin mercapto acid esters have the disadvantage that for any given mercaptoacid ester group, for example, isooctyl thioglycolate, the tin content of the dialkyltin salt, e.g., dibutyltin salt, remains fixed. Therefore, where a high tin content in the resin is required, it is necessary to use a large amount of organotin mercapto `acid ester to supply the necessary tin, and this can be costly. This is the inherent disadvantage that arises when the tin content is limited to the stoichiometric amount of tin that reacts with the organic moiety in forming the organotin compound.

STATEMENT OF THE 'INVENTION In accordance with this invention, there are provided less costly organotin mercaptoacid ester containing stabilizer compositions for polyvinyl chloride resins which have no mercaptan odor, are compatible with the resins, lessen development of early discoloration of the resin when heated at elevated temperatures, and have a controlled tin content, comprising (a) At least one diorganotin mercapto acid ester which has from one to two mercapto carboxylic acid ester groups having from two to about sixty carbon atoms, linked to tin through a mercapto sulfur atom, and two hydrocarbon groups having from one to about thirty carbon atoms, linked to tin through carbon and (b) An organotin complex derived from the reaction of a diorganotin oxide and an ester of an oxygen-containing acid.

Further, in accordance with the invention, there are provided homogeneous stable liquid stabilizer compositions comprising (a) and (b) above.

In the stabilizer combinations of the invention the tin content can be low or high, `and controlled within wide ranges, without limitation by stoichiometric requirements. The tin content of the stabilizer combination of the invention can be adjusted to within the range from 10% to 45%, from only slightly less than the corresponding organotin oxide, to only slightly more than the organotin mercaptocarboxylic acid ester. It can even be less than the ester, if desired, for special purposes, down to as low as 5%, but usually from 15% to 25% is preferred.

Control of tin content is obtained by any or all of the following techniques:

(l) By selection of the two components of appropriate tin contents,

(2) By adjusting the relative proportions of the more expensive organotin mercaptoacid ester and the less expensive organotin oxide-ester reaction product,

(3) By adjusting the amount of organotin oxide employed in reaction with the ester of the oxygen-containing acid to form the organotin oxide-ester reaction product (see the section entitled Proportions of Components in Stabilizer Combination, below).

Tis gives a very precise adjustment of tin content, never before so readily obtainable.

There are also provided, in accordance with the invention, polyvinyl chloride resin compositions consisting essentially of a polyvinyl chloride resin, a diorganotin mercapto acid ester, and an organotin complex derived from reaction of a diorganotin oxide and an ester of an oxygencontaining acid.

In addition, in accordance with the invention, a process for enhancing the resistance of polyvinyl chloride resins to the development of early discoloration is provided, which comprises incorporating with a polyvinyl chloride resin a diorganotin mercapto acid ester and an organotin complex derived from reaction of a diorganotin oxide and an ester of an oxygen-containing acid.

Still further in accordance with the invention, a process is provided for preparing organotin stabilizer combinations having a tin content controllable over a wide range without limitations imposed by stoichiometric considerations, which comprises combining a complex formed by the reaction of a diorganotin oxide and an ester of an oxygen-containing acid and having a tin content within the range from about 1 to about 50% by weight of the complex with a diorganotin mercapto acid ester, to provide an overall tin content in the mixture within the range from about 5 to about 45%.

The complex reaction products of the diorganotin oxides with the esters of the oxygen-containing acids act to enhance the eiectiveness of the organotin mercapto acid esters in improving resistance of polyvinyl chloride resins to development of early yellow discoloration which sets in during the first 'fifteen to thirty minutes of heating at 350 to 375 F. and they may at the same time improve the long term heat stability. This effect on early yellow discoloration is indeed surprising, inasmuch as the organotin oxideester complexes alone do not enhance resistance of polyvinyl chloride resins to development of early discoloration at high temperatures and, in fact, impart considerable early discoloration of their own to the resin. These diorganotin oxide-ester complexes further eliminate the disagreeable mercaptan odor when blended with the diorganotin mercapto-acid esters. Because of the lesser diorganotin mercapto-acid ester content in these stabilizer formulations, the overall mercaptan content is reduced and light stability and sulfide stain resistance improved and at the same time cost is reduced because of the inexpensive complex as compared to the organotin mercaptoacid esters.

The diorganotin oxide-ester complexes and the diorganotin mercapto acid esters can be liquids or solids. If liquid, they can be blended to form stable homogeneous solutions which have an advantage in that they can be metered out accurately and uniformly.

'Ihe organotin mercapto acid esters The diorganotin mercapto acid esters can be monomeric or polymeric, but are preferably monomeric. The monomers can be dened as diorganotln compounds having organic radicals linked to tin only through carbon, and

The S-Zl-COORa group is derived from a mercapto carboxylic acid ester.

m is the number of COORH groups and is an integer from one to four, preferably one to two.

R3 is an organic group derived from a monohydric or polyhydric alcohol having from one to about four hydroxyl groups and from about one to about thirty carbon atoms, preferaby from two to live carbon atoms, in the case of polyols, and from six to twenty-tive carbon atoms in the case of monohydric alcohols. If there is more than one COOR3 group, the R3 radicals can be the same or different.

R1 and R2 are hydrocarbon radicals which can be the same or different having from about one to about thirty carbon atoms, preferably from about three to about eight carbon atoms and can be selected from among alkyl, aryl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl and arylalkyl. R1 and R2 can, for example, be methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, amyl, hexyl, octyl, 2-ethylhexyl, iso-octyl, nonyl, isononyl, decyl, undecyl, lauryl, palmityl, stearyl, myristyl, behenyl, cyclobutyl, cyclohexyl, methyl cyclohexyl and cyclopentyl, phenyl, benzyl, cumyl, tolyl and xylyl.

Z1 is a bivalent organic radical carrying the S and COOR3 groups, and in addition can contain halogen, free carboxylic acid groups, keto groups, mercapto groups, carboxylic acid salt groups, ether groups and hydroxyl groups. The Z1 radical has from one to about thirty carbon atoms, and preferably from about one to about ve carbon atoms, such as an alkylene, arylene or cycloalkylene radical.

The S---Z1-(COOR3)m groups are derived from monoor polymercapto carboxylic acid esters by removal of the hydrogen atom of the mercapto group. These include the esters of aliphatic, aromatic, cycloaliphatic and heterocyclic acids which contain at least one mercapto group, and can also contain inert substituents such as halogen, hydroxyl, keto and alkoxy groups, such as `for example, esters of mercaptoacetic acid, mercaptopropionic acid, mercaptooleic acid, rnercaptoricinoleic acid, mercaptolinoleic acid, mercaptostearic acid, mercaptobutyric acid, mercaptovaleric acid, rnercaptohexanoic acid, mercaptooctanoic acid, thiolactic acid, mercaptolevulinic acid, mercaptolauric acid, mercaptobehenic acid, dithiotartaric acid, mercaptopalmitic acid, mercaptobenzoic acid, mercaptomethylbenzoic acid, mercaptocyclohexane carboxylic acid, mercaptofuroic acid, thiomalic acid, mercaptoglutaric acid, mcrcaptoazelaic acid, mercaptornalonic acid, mercaptoadipic acid, mercaptopimelic acid, mercaptosuberic acid, mercaptosebacic acid, mercaptophenylacetic acid and mercaptoterephthalic acid.

R3 is an organic group derived from a monohydric or polyhydric alcohol of the formula R4-(OH)4 where n4 is an integer from one to about four, but is preferably one or two. Thus, R4 can be alkyl, alkylene, alkenyl, aryl, arylene, mixed alkyl-aryl, mixed aryl-alkyl, cycloaliphatic and heterocyclic, and can contain from about one to about thirty carbon atoms, and can also contain ester groups, alkoxy groups, hydroxyl groups, halogen atoms and other inert substituents. Preferably, R4 is derived from a monohydric alcohol containing from one to about thirty carbon atoms, such as methyl, ethyl, propyl, nbutyl, t-butyl, isobutyl, octyl, isooctyl, Z-ethylhexyl, decyl, lauryl, octadecyl, myristyl, palmityl, oleyl, dodecyl, isotridecyl, and ricinoleyl alcohols, cyclic monohydric alcohols, such as cyclopropanol, 2,2-dimethyl-l-cyclopropanol, cyclobutanol, 2-phenyl-l-cyclobutanol, cyclopentanol, cyclopentenol, cyclohexanol, cyclohexenol, 2- methyl, 3-methyl-, and 4-methyl-cyclohexanol, 2-phenyl-cyclohexanol, 3,3,5-trimethyl cyclohexanol, 1,4-cyclohexadiene-3-ol, cycloheptanol, cycloheptene-B-ol, 1,5-cycloheptadiene-S-ol, 2-methyl-, 3-methyland 4-methyl cycloheptanol, cyclooctanol, cyclooctenol, cyclononanol, cyclodecanol, cyclodecene-S-ol, cyclododecanol, the paramethanols, such as 3-hydroxy-p-methane, 2-hydroxy-pmenthane, the para-menthenols such as a-terpineol, borneol, pine oil, fenchol, 2,2-di-methyl-3,r-cndo-methylene cyclohexanol, methyl borneol, 2,2,lO-trimethyl-3,6endo methylene cyclohexanol, the cyclic sesquiterphenols such as farnesol and nerolidol, the sterols such as cholesterol, dihydrocholesterol, ergosterol, 24-ethyl cholsterol, the condensed alicyclic alcohols such as l, and 2-hydroxy- 1,2,3,4-tetrahydronaphthalene and l-, and 2-hydroxydecahydronaphthalene, or from a dihydric alcohol such as glycols containing from two to about thirty carbon atoms, including ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, tetramethylene glycol, neopentyl glycol and decamethylene glycol, 2,2-4trimethyl pentane-diol, 2,2,4,4tetramethyl cyclobutane-diol, cyclohexane 1,4 dimethanol, 4,4-isopropylidene-dicyclohexanol, and polyols such as glycerine, triethylol propane, mannitol, sorbitol, erythritol, dipentaerythritol, pentaerythritol, and trimethylol propane.

Preferred monohydric alcohols are C6-C25 aliphatic alcohols and cyclohexanol. Preferred polyhydric alcohols are ethylene glycol, propylene glycol, neopentyl glycol, pentaerythritol and trimethylol propane.

The diorganotin thioglycolates, a and -mercaptopropionates and thiomalates are preferred as the organotin mercapto acid ester component, These are the most practical of the organotin mercapto acid esters from the standpoint of availability, cost and performance. These diorganotin mercapto acid esters are mostly liquids and are compatible with polyvinyl chloride resins and other stabilizers therefor, and form homogeneous solutions with the diorganotin oxide-ester complexes.

The diorganotin mercaptoacid esters, where not known, can be readily prepared by reaction of the mercaptocarboxylic acid esters with the corresponding organotin oxide or chloride. For a more complete explanation of the process for making, and for additional examples of, these organotin mercapto ester compounds, see U.S. Pats. Nos. 2,648,650 to Weinberg et al., 2,641,596 and 2,752, 325 to Leistner, and 3,115,509 to Mack, and Canadian Pat. No. 649,989 to Mack.

The organotin mercapto acid esters containing two different mercapto acid ester groups can be prepared by reacting the desired organotin oxide or chloride with a mixture of the mercapto acid esters, or by heating the two different organotin esters together.

`Polymer-ic diorganotin mercaptoacid esters can be dened by the formula:

wherein R1, R2, R3 and Z1 are as dened previously and wherein Z2 is a bivalent group, such as sulfur, a mercapto acid group, or a mercapto alkanol group, and n3 is a number from one to about twenty.

The Z2 mercapto acid group can have the formula: -S-Zl-COO and the Z2 mercaptoalkanol group can have the formula:

The lfollowing diorganotin mercapto carboxylic acid esters are typical of those coming within the invention:

s-cuza-cobcibcnaoa csan The organotin oxide-ester reaction products The diorganotin oxides useful in preparing the organotin oxide-ester complexes employed in this invention contam organic groups linked to tin only through carbon, and can be represented by the following formula:

SnO R2.

III

Each compound contains per tin atom two hydrocarbon radicals (R1 and R2) having from about one to about thirty carbon atoms, preferably from about three to about eight carbon atoms, which can be selected from among alkyl, alkenyl, aryl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl and arylalkyl. R1 and R2 can, for example, be methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tertbutyl, sec-butyl, amyl, hexyl, octyl, 2-ethylhexyl, lso-octyl, isononyl, nonyl, decyl, undecyl, lauryl, palmltyl, stearyl, myristyl, behenyl, phenyl, benzyl, cumyl, tolyl, xylyl, cyclobutyl, cyclohexyl, methyl cyclohexyl, and cyclopentyl.

Examples of organotin oxides which can be employed in preparing the organotin oxide-ester complexnnclude, but are not limited to, dimethyltin oxide, diethyltin oxide, dipropyltin oxide, dibutyltin oxide, diamyltmoxtde, d1- octyltin oxide, didecyltin oxide, dilauryltm o xidendlpropenyltin oxide, diphenyltin oxide, dinaphthyltm ox1de, d1 tolyltin oxide, methylethyltin oxide, phenylbutyltin oxide, dibenzyltin oxide, dixylyltin oxide, dicyclobutyltm oxide, dicyclohexyltin oxide, methylcyclohexyltin oxide, and d1- cumyltin oxide.

The esters which are employed for reactlon with the organotin oxide are esters of an organic monocarboxyllc or polycarboxylic acid or an inorganic oxygen-contaimng acid and a monohydric or polyhydric alcohol or phenol. Such organic acid esters include aliphatic, cycloahphatic and aromatic carboxylic acid esters of aliphatic, cycloaliphatic, and aromatic monohydric or polyhydric alcohol or phenol, and contain from two to about one thousand carbon atoms and one to about six carboxylic acid ester groups. Exemplary esters which can be employed are known, and are disclosed in U.S. Pats. Nos. 2,597,920 to Carroll and 2,763,632 to Johnson, which disclosures are incorporated herein by reference.

The esters of oxygen-containing acids useful in this invention include, but are not limited to, ethyl ortho silicate, triethyl arsenate, n-propyl nitrate, n-octyl nitrate, o-cresyl p toluene sulphonate, cyclohexyl p-toluene sulphonamide, di-n-propyl sulfate, di-n-dodecyl sulfate, trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, tr-ibutylphosphate, triisobutyl phosphate, triamyl phosphate, tri-o-cresyl phosphate, tri-p-cresyl phosphate, tri-m-cresyl, phosphate, triphenyl phosphate, trixylyl phosphate, butyl di-(-methoxyethyl) phosphate, butyl di(ethoxyethy1) phosphate, sorbityl hexaphosphate, amyl iborate, methyl acetate, ethyl acetate, n-propylacetate, isopropyl acetate, butyl acetate, m-cresyl acetate, phenyl acetate, ethylene glycol diacetate, diglycerol tetraacetate, glycerol monolactate acetate, methyl propionate, n-butyl propionate, sec-butyl propionate, ethylene glycol dipropionate, triethylene glycol dipropionate, ethyl lbutyrate, n-propyl butyrate, butyl butyrate, pentyl butyrate, 2- propenyl butyrate, hexyl butyrate, ethylene glycol dibutyrate, ethyl laurate, phenyl laurate, ethyl stearate, butyl stearato, ethyl palmitate, Z-naphthyl lactate, ethyl benzoate, -naphthyl benzoate, benzyl benzoate, methylo-benzoyl benzoate, ethyl-o-benzoyl benzoate, amyl benzoate, sorbityl hexabenzoate, diethyl oxalate, dibutyl oxalate, diethyl oxalate, diamyl oxalate, dimethyl maleate, diethyl maleate, dipropyl maleate, dioctyl maleate, dilauryl maleate, diethyl maleate, dipropenyl maleate, ethyl adipate, di-butyl adipate, ethoxyethyl adipate, ethyl sebacate, dibutyl sebacate, ethyl succinate, butyl succinate, triethyl citrate, tributyl citrate, butyl tartrate, dibutyl tartrate, diamyl tartrate, dimethyl phthalate, diethyl phthalate, propyl phthalate, dibutyl phthalate, diamyl phthalate, dioctyl phthalate, diisooctyl phthalate, butyl glycol phthalate, diphenyl phthalate, methoxyethyl phthalate, butoxyethyl phthalate, dimethyl cyclohexyl phthalate, methyl phthalyl ethyl glycolate, ethyl phthalyl ethyl glycolate, butyl pthalyl butyl glycolate, methyl salicylate, phenyl salicylate, dioctyl thiodipropionate and dithiobis(isooctyl propionate) The diorganotin oxide-ester complexes can be prepared by reacting an organotin oxide with an ester under conditions of elevated temperature and for a suicient period of time to elect complete reaction therebetween. Complete descriptions of the preparation of these reaction products are disclosed in the Johnson and Carroll patents discussed above, the disclosures of which are incorporated herein by reference.

Optional stabilizers If desired, a bivalent stannous tin salt can be employed with the stabilizer combination of the invention, as disclosed in application Ser. No. 743,972, led July ll, 1968. The stannous salt contains two groups selected from the group consisting of bromide and chloride and non-nitrogenous organic groups which are the residue of non-nitrogenous organic compounds having an active hydrogen attached to oxygen or sulfur which is replaceable by a metal, specifically tin.

The organic stannous salts which can be employed according to the present invention preferably include stannous salts of carboxylic acids, alcohols, phenols `and mercaptides. The stannous salts can also comprise mixtures of anions, e.g., carboxylate and phenolate. The stannous salts enhance the stabilizing effectiveness of the combination of the organotin mercapto acid ester-organotin oxide-ester complex.

The stabilizer combination of this invention can also be used in combination with other known stabilizers,

such as phenolic antioxidants, as disclosed in U.S. Pat. No. 3,346,536, organic phosphite esters, as disclosed in U.S. Pat. No. 3,346,536, epoxy compounds as disclosed in U.S. Pat. No. 2,997,454, as well as organometallic compounds such as alkyltin sulfdes, such as mono or dibutyltin sulfide and dioctyltin sulfide. Other organometallic stabilizers include polyvalent metal salts of medium and of high molecular weight fatty acids and phenols, with metals such as calcium, tin, cadmium, barium, zinc, magnesium and strontium.

Plasticizers and other additives The stabilizing compositions of this invention, both with and without supplementary stabilizers, are excellent stabilizers for both plasticized and unplasticized polyvinyl chloride resins but particularly for unplasticized resins. When plasticizers are to be employed, they may be incorporated into the polyvinyl chloride resins in accordance with conventional means. The conventional plasticizers can be used, such as dioctyl phthalate, dioctyl sebacate and tricresyl phosphate or any of the esters mentioned hereinbefore with respect to the organotin oxideester complex. The amount of plasticizer employed with the resin is dependentupon the form of resin desired. Thus, rigids are formed employing up to about plasticizer by weight of resin; semi-rigids are formed employing from about 10 to about 18% plasticizer by weight of resin, and plasticized resins are formed employing from about 18 to about 75% plasticizer by weight of resin.

Particularly useful plasticizers are the epoxy higher esters having from about twenty to about one hundred fifty carbon atoms. Such esters will initially have had unsaturation in the alcohol or acid portion of the molecule, which is taken up by the formation of the epoxy group.

A small amount, usually not more than 1.5%, of a parting agent or lubricant, also can be included. Typical parting agents are the higher aliphatic acids, and salts having twelve to twenty-four carbon atoms, such as stearic acid, lauric acid, palmitic acid and myristic acid, lithium stearate and calcium palmitate, mineral lubricating oils, polyvinyl stearate, polyethylene, paraffin wax and montan wax derivatives.

Impact modifiers, for improving the toughness or irnpact-resistance of unplasticized resins, can also be added to the resin compositions stabilized by the present 1nvention in minor amounts of usually not more than 10% Examples of such impact modifiers include chlorinated polyethylene, ABS polymers, and polyacrylate-butadiene graft copolymers.

Polyvinyl chloride resins The invention is applicable to any polyvinyl chloride resin. The term polyvinyl chloride as used herein is inclusive of any polymer formed at least in part of the and having a chlorine content in excess of 40%. In this group, the X groups can each be either hydrogen or chlorine. In polyvinyl chloride homopolymers, each of the X groups is hydrogen. Thus, the term includes not only polyvinyl chloride homopolymers but also after-chlorinated polyvinyl chlorides such as those disclosed in British Pat. No. 893,288 and also copolymers of vinyl chloride in a major portion and other copolymerizable monomers in a minor proportion, such as copolymers of vinyl chloride and vinyl acetate, copolymers of vinyl chloride with maleic or fumaric acids or esters, and copolymers of vinyl chloride with styrene, propylene, and ethylene. The invention also is applicable to mixtures of polyvinyl chloride in a major proportion with other synthetic resins such as chlorinated polyethylene or a copolymer of acrylonitrile, butadiene and styrene. Among the polyvinyl chlo- 12 rides which can be stabilized are the uniaxially-stretch oriented polyvinyl chlorides described in U.S. Pat. No. 2,984,593 to Isaksem et al., that is, syndiotactic polyvinyl chloride, as well as atactic and isotactic polyvinyl chlorides.

Proportion of components of stabilizer combinations The essential components of the stabilizer combination of the invention, the diorganotin mercapto acid ester and the diorganotin oxide-ester complex, are mixed in proportions to provide a tin content which, in the amount of stabilizer combination used, usually from 0.25 to 10%, preferably from 0.5% to 5%, by weight of the resin, is sufficient to impart the desired resistance to development of early discoloration at working temperatures of 350 F. or 375 F. The amount of diorganotin complex that imparts this improvement to the diorganotin mercapto acid ester is determined in each case by trial and error, adding the complex in small amounts, until the effect is obtained. The amount of complex is not in any case so large that the effect is not obtained, at the amount of stabilizer used in the resin.

The diorganotin mercapto acid ester is the principal stabilizer component, and the proportion of this component that is to be used is determined by the desired stabilizing effect characteristic of this component. The tin content of any specific diorganotin mercapto acid ester is of course fixed, and after the desired amount of this component has been established, the tin content of the total composition is adjusted upwardly or downwardly by addition of the appropriate amount of diorganotin oxide-oxygen-containing acid ester complex. The tin content of this complex can be easily adjusted by selecting the proportions of dialkyltin oxide and ester to be reacted. No stoichiometry is required. Thus, a very wide range of tin contents in the stabilizer combination is possible even if one imposes limitations on the specific diorganotin oxide to be used and the particular diorganotin mercapto acid ester to be used.

It is possible to formulate stabilizer combinations containing from about l0 to about 90% diorganotin mercapto acid ester and from about l0 to about 90% diorganotin oxide-oxygen-containing acid ester complex. The amounts of each are always selected to obtain an enhanced resistance to the development of early discoloration when the resin is heated at 350 F. to 375 F. This amount is to some extent dependent on tin content, and to some extent on the proportion of diorganotin mercapto acid ester, and the two are also correlated with the particular compounds of each type that are used. Thus, it may be desirable to maintain a higher proportion of diorganotin mercapto acid ester in some stabilizer systems, as well as a higher tin content, to obtain the enhanced resistance to early discoloration. This can be achieved by combining a relatively small amount of diorganotin oxideester of an oxygen containing acid complex, whose tin content is very high with the diorganotin mercapto acid ester. Such high tin containing ester complexes are easily prepared because the amounts of diorganotin oxide and ester employed in forming this complex can be varied considerably. Up to two moles of organotin oxide per mole of ester group will react to form the desired cornplex. Thus, the diorganotin oxide-ester complex can contain as little as 1% tin, up to about 50% tin, and preferably from about 10i to about 30% tin.

This means that the tin content of the stabilizer combination can be adjusted to contain about 5 to about 45% of tin, preferably from about 10% to about 30% tin. It will be apparent that the stabilizer combination can have a lower or higher tin content than, or the same tin content as, the diorganotin mercapto acid ester. Thus, the tin content in the stabilizer combination can be high or low, and can be controlled within wide ranges without limitation by stoichiometric requirements.

The molar ratio of the tin in the diorganotin oxideester complex to the tin in the diorganotin mercapto acid ester should be within the range of from about 0.05:1 to about 1.5:l, and preferably within the range of from about 0.25 :1 to about 1:1.

'If a stannous salt is to be added to the stabilizer composition, the amount of stannous tin in the stannous salt can be as little as about 0.5% by weight of the tin in the diorganotin mercapto acid ester. Too high a proportion of stannous salt can/ decrease elfectiveness of the stabilizer combination rather than increase it. The preferred amount of stannous tin is from about 1% to about 8% by weight of the tin in the diorganotin mercapto acid ester.

Proportions of stabilizers in resin The more rigorous the conditions to which the resin is subjected during Working and mixing and the longer the term required for resistance to degradation, the larger the amount of stabilizer required.

Generally as little as 0.25% total of the stabilizer combination by weight of the resin provides suicient tin to impart some resistance to heat deterioration, and this may be adequate in many cases. There is no critical upper limit on the amount of the stabilizer combination but amounts above about 10% by weight of the resin do not give an increase in stabilizing effectiveness commensurate with the additional stabilizer employed. Preferably, the amount is from about 0.5 to about by weight of the resin.

The stabilizer combination of the invention can be employed together with other polyvinyl chloride resin stabilizers. The stabilizer combination of the invention in this event will be the major stabilizer, and the additional stabilizers will supplement the stabilizing action of the former, the amount of the stabilizer combination being within the range from about 0.25 to about 15 parts by weight per 100 parts of the resin, and the additional stabilizers being in an amount of from about 0.05 to about parts per 100 parts of the resin.

Preparation and processing Generally, the stabilizer composition of this invention can be prepared by mixing, blending or dissolving the diorganotin mercapto acid ester with the diorganotin oxide-ester complex, to form a homogeneous mixture or the individual components of the composition can be compounded separately into the resin as can other ingredients of the formulation.

The stabilizer combination of the invention can be formulated and marketed as a liquid or solid composition for incorporation in the resin by the resin manufacturer or by the converter. The liquid compositions are homogeneous solutions which are stable and show no tendency to separate on long standing.

The preparation of the polyvinyl chloride resin composition is easily accomplished by conventional procedures. The selected stabilizer combination is compounded with the polyvinyl chloride resin, and other ingredients of the formulation and heated on a two or three roll mill, at a temperature at which the mix is iluid and thorough blending facilitated, milling the resin composition inc1uding any plasticizer at from 250 to 375 F. for a time suicient to form a homogeneous mass, five minutes, usually. After the mass is uniform, it is sheeted off in the usual way.

The following examples relate to the preparation of diorganotin oxide complexes with esters of oxygen-containing acid.

EXAMPLE A Dibutyltin oxide (39 g.) and diisooctyl phthalate (61 g.) were mixed together and heated at about 190 C., until the dibutyltin oxide dissolved, which required about 3 hours. The homogeneous liquid was then cooled. The dibutyltin oxide-diisooctyl phthalate complex contained 18.6% Sn.

14 EXAM-PLE B Dibutyltin oxide (249 g.) and diisooctyl phthalate (353 g.) were mixed together and heated at about 190 C., until the dibutyltin oxide dissolved, which required about 3.5 hours. The homogeneous liquid was then cooled. The dibutyltin oxide-diisooctyl phthalate complex contained 19.7% Sn.

EXAMPLE C Dibutyltin oxide (249 g.) and tridecyl phosphite (542 g.) were mixed together and heated at about 190 C., until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dibutyltin oxide-tridecyl phosphite complex contained 15.0% Sn.

EXAMPLE D Dibutyltin oxide (24.9 g.) and dithiobis(octylpropio nate) 38.9 g.) were mixed together and heated at about 190 C., until the dibutyltin oxide dissolved, which required about 3.5 hours. The homogeneous liquid Was then cooled. The dibutyltin oxide-dithiobis(octylpropionate) complex contained 18.6% Sn.

EXAMPLE E EXAMPLE F Dibutyltin oxide (249 g.) and dioctyl maleate (351 g.) were mixed together and heated at about 185 C., until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dibutyltin oxidedioctyl maleate complex contained 19.8% Sn.

EXAMPLE G Dibutyltin oxide (159- g.) and diisooctyl phthalate 159 g.) were mixed together and heated at about 190 C., until the dibutyltin oxide dissolved, which required about 3.3 hours. The mixture was then cooled and a homogeneous viscous liquid complex was formed. The dibutyltin oxide-diisooctyl phthalate complex contained 23.85% Sn.

EXAMPLE H Dibutyltin oxide (24.9 g.) and dioctyl thiodipropionate (38.9 g.) were mixed together and heated at about 180 C., until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dibutyltin oxide-dioctyl thiodipropionate complex contained 18.6% Sn.

EXAMPLE I Dibutyltin oxide (24.9 g.) and dithiobis(diisoocty1 acetate) (38.9 g.) were mixed together and heated at about 175 C., until the dibutyltin oxide dissolved, Which required about 3.5 hours. Upon cooling, a homogeneous brown liquid complex was formed. The dibutyltin oxidedithiobis(tridecyl phosphite) complex contained 18.6% Sn.

EXAMPLE K Dibutyltin oxide (24.9 g.) and isooctyl epoxy tallate (Drapex 4.4) (38.9 g.) were mixed together and heated at about C., until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous (yellow) liquid was then cooled. The dibutyltin oxide-isooctyl epoxy tallate (Drapex 4.4) complex contained 18.6% Sn.

EXAMPLE L Dibutyltin oxide (24.9 g.) and tridecyl phosphite (38.9 g.) were mixed together and heated at about C until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dibutyltin oxide-tridecyl phosphite complex contained 18.6% Sn.

EXAMPLE M Dibutyltn oxide (24.9 g.) and diethylene glycol dibenzoate (Benzoflex 245) (38.9 g.) were mixed together and heated at about 140 C., until the dibutyltin oxide dissolved, which required about 3 hours. The homogeneous liquid was then cooled. The dibutyltin oxide-diethylene glycol dibenzoate complex contained 18.6% Sn.

EXAMPLE N Dibutyltn oxide (24.9 g.) and triethylene glycol di-2- ethyl hexoate (Flexol 3-GO) (38.9 g.) were mixed together and heated at about 170 C., until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dibutyltin oxidetriethylene glycol di2ethyl hexoate complex contained 18.6% Sn.

EXAMPLE O Dibutyltn oxide (24.9 g.) and polyethylene glycol di-2-ethyl hexoate (Flexol 4-GO) (38.9 g.) were mixed together and heated at about 185 C., until the dibutyltin oxide dissolved, which required about 3:5 hours. The homogeneous liquid was then cooled. The dibutyltin oxidepolyethylene glycol di2ethyl hexoate complex contained 18.6% Sn.

'EXAMPLE P Dibutyltn oxide (99.6 g.) and diisooctyl phthalate (39.0 g.) were mixed together and heated to about 190 C., until the dibutyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled to room temperature. The dibutyltin oxide-diisooctyl phthalate complex contained about 34.3% Sn and was a solid paste at room temperature.

EXAMPLE Q Dioctyltin oxide (72.2 g.) and dioctyl phthalate (75.8 g.) were mixed together and heated at about 185 C., until the dioctyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dioctyltin oxide-dioctyl phthalate complex contained 16.8% Sn.

EXAMPLE R Dimethyltin oxide (16.5 g.) and diisooctyl phthalate (47.4 g.) were mixed together and heated at about 185 C., until the dimethyltin oxide dissolved, which required about 4 hours. The homogeneous liquid was then cooled. The dimethyltin oxide-diisooctyl phthalate complex contained 18.7% Sn.

EXAMPLE S Dioctyltin oxide (48 g.) and dioctyl phthalate (52 g.) were mixed together and heated at about 185 C., until the dioctyltin oxide dissolved, which required about 3.5 hours. The homogeneous liquid was then cooled. The dioctyltin oxide-dioctyl phthalate complex contained 15.7% Sn.

EXAMPLE T Dibutyltn oxide (50 g.) and epoxy soyabean oil (Drapex 6.8) (50 g.) were mixed together and heated at about 185 C., until the dibutyltin oxide dissolved, which required about 4 hours. A homogeneous viscous liquid forms on cooling. The dibutyltin oxide-epoxy soyabean oil complex contained 23.8% Sn.

The following examples relate to the preparation of various stabilizer compositions in accordance with the invention.

EXAMPLE l Dibutyltn bis(sooctyl thioglycolate) (65 parts) was blended with the dibutyltin oxide-diisooctyl phthalate complex of Example A (35 parts) at 25 C., forming a homogeneous liquid composition which contained about 18.6% Su, and was useful as a stabilizer composition for polyvinyl chloride resins, capable of lessening the development of early discoloration when heated at 350 to 375 F.

EXAMPLE II yDibutyltn bis(isoocty1 mercaptopropionate) (65 parts) was blended with the dibtuyltin oxide-diisooctyl phthalate complex of Example B (35 parts) at 25 C. forming a homogeneous liquid composition which contained about 18.6% Sn and was useful as a stabilizer composition for polyvinyl chloride resins, capable of lesseniug the development of early discoloration when heated at 350 to 375 F.

EXAMPLE III Dibutyltn bis(isooctyl thioglycolate) (65 parts) was blended with the dibutyltin oxide-diisooctyl phthalate complex of Example G (35 parts) by stirring the lmixture at 25 C. forming a homogeneous liquid composition which contained about 20.45% Sn and was useful as a stabilizer composition for polyvinyl chloride resins, capable of lessening the development of early discoloration when heated at 350 to 375 F.

EXAMPLE IV Dibutyltn bis (isooctyl mercaptopropionate) (73 parts) was blended with the dibutyltin oxide-diisoctyl phthalate complex of Example B (27 parts) at 25 C. forming a homogeneous liquid composition which contained about 18.3% Sn and was useful as a stabilizer composition for polyvinyl chloride resins, capable of lessening the development of early discoloration when heated at 350 to 375 F.

EXAMPLE V vDioctyltin bis(isooctyl thioglycolate) (65 parts) was blended with the dioctyltin oxide-diisooctyl phthalate complex of lExample Q (35 parts) at 25 C. forming a homogeneous liquid composition which contained about 16.8% Sn and was useful as a stabilizer composition for polyvinyl chloride resins, capable of lessening the development of early discoloration when heated at 350 to 375 F.

EXAMPLE VI EXAMPLE 1 Rigid polyvinyl chloride resin formulations were prepared having the following composition:

Parts by weight Polyvinyl chloride homopolymer (Plaskon 313) n-Octyldecyl phthalate (Elastex 82P Allied Chemical) 4.0 Lubricant (Wax E) 0.2 Stabilizers (1) 1 Noted in Table I below.

The ingredients were blended and the mixture was compounded, then heated on a two-roll mill at 350 F., for 5 minutes, sheeted off, and cut into strips. The strips were placed in an air oven heated to 375 F. and 350 F. and samples removed at -fifteen minute intervals and attached to cards. The yappearance of the samples on the cards is noted in Table I, below.

TABLE I Example Control A Amt. Control B Amt. Example l Amt.

Stabilizer composition (parts) Dibutlytin bis (isooctyl 1. Dibutyltin oxide-diisoetyl 1. 0 Dlbutyltln bis (isooetyl thio- 0.65 thioglycolate). phthalate complex glycolate). Dibutyltin 0. 35

(Example A). oxide-diisooctyl phthalate complex (Example A).

Time (min.) Color Color Color Temperature, 375 F.

Initial Colorless Very pale yellow Colorless.

...... Yellow O Do.

d Pale yellow.

Y llo Do: Very pale yellow. Lighli yellow.

do 120 Dark yellow, brown edges Red Do.

EXAMPLE 2 Rigid polyvinyl chloride resin formulations were prepared having the following composition:

Control A shows that the dibutyltin bis(isooctyl thioglycolate) is an eiective heat stabilizer.

Control B shows that dibutyltin oxide-diisooctyl phthalate complex alone is not a very effective stabilizer, inasmuch as the resin turns deep red after heating for and 30 60 minutes, at 375 F. and 350 F., respectively, and is n ldecyl phthalate (Elasx 82p Allied Cheml 4 o already considerably discolored after l5 minutes of heat- Lubricag) 0'2 ing. However, Example 1 clearly indicates that even small Stabilizers (i) amounts of the dibutyltin oxide-diisooctyl phthalate complex enhance the effectiveness of dibutyltin bis(isooctyl 1Ntedm Table II below' thioglycolate) iIl greatly improving resistance 0f POlY- The ingredients were blended and the mixture was vinyl chloride resin to development of early discoloration compounded, then heated on a tw0 r011 mju at 350 E, at 375 and 350 F- After 15 IIIDUGS 0f heating at for live minutes, sheeted olf, and cut into strips. The strips 375 P'-, EXamPle l remained COlOfleSS, Whereas COHU'OIS were placed in `an air oven heated to 375 F. and 350 F.

P-arts by weight Polyvinyl chloride homopolymer (Plaskon 313) 100 A and B were quite yellow. -Exarnple 1 was less discolored 40 and samples removed at 15 minute intervals and attached even after 30 minutes of heating than was Control A after to cards. The appearance of the samples on the cards is the iirst 15 minutes of heating. noted in Table II, below.

TABLE II Example Control C Amt. Control B Amt. Example 2 Amt.

Stabilizer composition Dibutyltin bis isooetyl 1.0 Dibutyltin oxide-diisooctyl 1.0 Dibutyltin bis(isooctyl mercaptopro- 0.65

mercaptopropionate). phthalate (Example A). 'onat p1 Dibutyltln oxide-disoootyl phthalate 0.35

complex (Example A).

Time (min.) Color Color Color Temperature, 375 F.

Temperature, 350 F.

Initial Colorless Very pale yellow Colorless. 15 Dark yellow Do. Yellow-orange. Do. Orange Do. Red-orange Do.

d Pale yellow. Red Do. Bed Light yellow. 120 Dark yellow, brown edges Red Do.

Example 1, after minutes and 60 minutes respective- Control C shows that the dibutyltin bis(isoocty1 merly of heating at 350 F., was still virtually colorless, 70 captopropionate) is `an effective heat stabilizer. whereas Control A was yellow. After minutes of heat- Control B shows that dibutyltin oxide-diisooctyl phthaling at 350 F., Example 1 is only very pale yellow and ate complex alone is not a very effective stabilizer, inasless discolored than ControlA after 15 minutes of heating. much as the resin turns deep red after heating for 30 The improvement in resistance to early discoloration is and 60 minutes, at 375 F. and 350 F., respectwely,

quite apparent. Iand is already considerably discolored after 15 minutes of heating. However, Example 2 clearly indicates that even small amounts of the dibutyltin oxide-diisooctyl TABLE III Example Control D Amt. Control E Amt. Example 3 AmtJ Stabilizer composition-.." Dlbutyltln blsdsooctyl 2. Dlbutyltin oxlde-dilsooetyl 2. 0 Dibutyltln bis(isooctyl thioglycolate) 1. 3 thloglycolate). phthalate complex (Ex- Dibutyltin oxide-diisooetyl phthalate 0.7

ample A). (Example A).

Time (mln.) Color Color Color Temperature, 375 F.

Very pale yellow Cologess.

o. Very pele yellow. Pale yellow.

Yellow o. Yellow-brown edges Reddlsh-brown.

Temperature, 350 F.

Very pale yellow- Light orange do phthalate complex enhance the eiectiveness of dibutyltin bis(soocty1 mercaptopropionate) in greatly improving resistance of polyvinyl chloride resin to development of early discoloration at 375 F. and 350 F. After l5 minutes of heating at 375 F., Example 2 remained colorless, whereas Controls C and B are quite yellow. Example 2 was less discolored even after 30 minutes of heating than was Control C after the rst minutes of heating.

Example 1, after 45 minutes and 60 minutes, respectively, of heating at 350 F., is still virtually colorless, whereas Control C is yellow.

The improvement in resistance to discoloration is quite apparent.

EXAMPLE 3 Rigid or nonplasticized polyvinyl chloride resin formulations were prepared having the following composition:

Parts by weight EXAMPLE 4 Rigid or non-plasticized polyvinyl chloride resin formulations were prepared having the following composition:

Parts by weight Polyvinyl chloride homopolymer (Solvic 229) 100 Lubricant (Wax E) 0.25 Stabilizers, noted in Table IV, below.

The stabilizer combination was blended with the resin 1 Noted in Table III, below. noted in Table IV below.

TABLE IV Example Control F Amt. Control G Amt. Example 4 .Amt

Stabilizer composition Dioetyltin bls(lsooctyl 1. 5 Dioetyltin oxide-dieetyl 1. 5 Dioetyltln bis(isooetyl thioglycolate). 1. 4 thioglycolate). phthalate complex (Ex- Dioctyltin oxide-dioctyl phthalate O. 1

ample S) (Example S).

Time (min.) Color Color Color Temperature, 375 I".

Colorless Very pale yellow- Colorless.

Orange Do.

Very pale yellow.

Dark brown.-.

Red... Red...

I Dark red Yellow, brown edges. Dark brown.

The ingredients were blended and the mixture was compounded, then heated on a two-roll mill Iat 350 F., for 5 minutes, sheeted off, and cut into strips. The strips were placed in air ovens heated to 375 F. and 350 F.

It is evident from the above results that the combination of dioctyltin oxide-dloctyl phthalate complex and dioctyltin bis(isooctyl thioglycolate) greatly improved the resistance to development of early discolororation at 375 and samPlQS ,removed at fifteen minute intervals and F. of polyvinyl chloride resins (Solvic 229).

modifier (Blendex 401) Lubricant (Wax E) 0.25 Stabilizer (l) 1 Noted in Table V below.

The ingredients were blended and the mixture was compounded, then heated on a two-roll mill at 350 F. for 'tive minutes, sheeted 01T, and cut into strips The strips were placed in an air oven, heated to 375 F. and samples removed at fteen minute intervals and affixed to a card. The appearance of the samples on the card is noted in Table V below.

22 EXAMPLE 6 Rigid polyvinyl chloride resin formulations were prepared having the following composition:

Parts by weight Polyvinyl chloride homopolymer (Diamond 100 Acrylonitrile-butadiene styrene copolymer, impact modier (Blendex 401) 10 Lubricant (Wax E) 0.25 Stabilizers (1) 1 Noted in Table VI below.

The ingredients were blended and the mixture was compounded, then heated on a two-roll mill at 350 F. for live minutes, sheeted off and cut into strips. The strips were placed in an air oven, heated to 375 F. and samples removed at fteen minute intervals and affixed to a card.

TABLE V Example Control H Parts Control J 1?arts Example 5 Parts Stabilizer eomposition. Dibutyltin bls-(isooetyl 2. 0 Dibntyltin oxide-diisooety 2. 0 Dibutyltin bis (sooetyl thoglyco- 1. 17

thioglycolate). phthalate complex late).

(Example G). Dibutyltin oxide-dlisooetyl phthalate 0.63

complex (Example G).

Tlme (min.) Color Color Color Initial Colorless Very pale yellow Colorless. 15.- Yellow range Do. 30....- ..do Orange-red.. Very pale yellow. o ed Pale yellow. Yellow, slight brown edge Black..- Yellow. 75 Yellow-brown Yellow-brown. 90 Dark brown Dark brown.

The results in Table V show that 1.8 parts of the stabilizer combination of the invention, namely, dibutyltin The appearance of the samples on the card is noted in Table VI below.

TABLE VI Example Control H Parts Controlt Parts Example 5 Parts Stabilizer composltion Dlbutyltin bis-(isooetyl 2. 0 Dlbutyltln oxidediisooctyl 2. 0 Dibntyltin bis (lsooctyl thioglyco- 1. 2

thioglycolate). phthalate complex lat (Example P). Dlbutyltln oxidedlisooetyl phthalate 0. 4

complex (Example P).

Time (min.) Color Color Color Colorless Very pale yellow Colorless.

Yellow range Yellow-brown.- Dark brown Dark brown.

bis(isooctyl thioglycolate) (1.17 parts) and dibutyltin oxide-diisooctyl phthalate complex (0.63), is superior in inhibiting development of early discoloration of polyvinyl chloride resin upon heating at 375 F. than larger amounts of the individual components thereof, namely, 2.0 parts of dibutyltin bis(isooctyl thioglycolate) alone (Control H) and 2.0 parts of dibutyltin oxide-diisooctyl phthalate complex alone (Control J).

The results in Table VI show that 1.6 parts of the stabilizer combination of the invention, namely, dibutyltin bis(isooctyl thioglycolate) (1.2 parts) and dibutyltin oxide-diisooctyl phthalate complex (0.4), is superior in inhibiting development of early discoloration of polyvinyl chloride resin upon heating at 375 F. th-an larger amounts of the individual components thereof, namely, 2.0 parts of dibutyltin bis(isooctyl thioglycolate) yalone (Control H) and 2.0 parts of dibutyltin oxide-diisooctyl phthalate complex alone (Control J).

EXAMPLE 7 Rigid polyvinyl chloride resin formulations were prepared having the following composition:

Parts by weight 1 Noted in Table VII below.

The ingredients were blended and the mixture was compounded, then heated on a two-roll mill at 350 F., for

24 EXAMPLE s Rigid polyvinyl chloride resin formulations were prepared having the following composition:

Parts by weight Polyvinyl chloride homopolymer (Diamond 40) 100 Acrylonitrile-butadiene-styrene copolymer, impact modifier (Blendex 401) 10 Lubricant (Wax E) 0.25 Stabilizers 1 Noted iu Table VII, below.

The ingredients were lblended and the mixture was compounded, then heated on a two-roll mill at 350 F., for ve minutes, sheeted off, and cut into strips. The strips were placed in an air oven heated to 375 F. and samples removed at minute intervals.

TABLE VIII Example Control M Parts Control N Parts Example 8 Parts Stabilizer composition- Dimethyltin oxidedioctyl- 2. 0 Dibutyltin bis (isooctyl 2. 0 Dibutyltiu bis(isooetyl thioglycolate). l. 3 phthalate complex thioglycolate). Dimethyltin oxide-dioctyl phthalate 0. 7 (Example R). (Example R).

Time (min.) Color Color Color Initial Severe discoloration within Colorless Colorless.

minu s. 15 Yellow Very pale yellow.

do Pale yellow. do Do. Yellow-brown edge Do. Yellow-brown Yellow-brown. Brown Brown.

tive minutes, sheeted off, and cut into strips. The strips were placed in an air oven heated to 375 F. and 350 F. `and samples removed at fifteen minute intenvals and attached to cards. The appearance of the samples on the cards is noted in Table VII, below.

The results in Table VIII clearly indicate that the combination `of dimethyltin oxide-dioctyl phthalate complex and dibutyltin bis(isooctyl thioglycolate) was effective in improving resistance of polyvinyl chloride resin to discoloration.

TABLE VII Example Control K Parts Control L Parts Example 7 Parts Stabilizer composition. Dioctyltin bis (isooctyl 2. 0 Dioctyltin oxide-diisooctyl 2. 0 Dioctyltln bis(isooctyl thioglycolate). 1. 3 thioglycolate). phthalate complex Dioetyltin oxide-diisooctyl phthalate 0. 7

(Example Q.) complex (Example Q).

Time (min.) Color Color Color Temperature, 375 F.

Colorless Very pale yellow Colorless. Yellow Orange Very pale yellow.

do do Pale yellow. do Red Yellow.

Yellow, slight brown edge Black Yellow, slight brown edge. Reddish-brown Reddish-brown. Brown Brown.

Temperature, 350 C.

Very pale yellow Colorless.

The results in Table VlI clearly show the improved effectiveness obtained by the stabilizer combination of the invention (taken at 2.0 parts per parts resin) over corresponding amounts of the dioctyltin bis(isooctyl thioglycolate) alone. It is clearly seen that the dioctyltin oxidediisooctyl phthalate complex enhances the effectiveness of the dioctyltin bis (isooctyl thioglycolate) in Light orange..

inhibiting development of early discoloration of the resin. 75

Do. Very pale yellow.

EXAMPLES 9-16 Polyvinyl chloride resin compositions were stabilized with combinations of dibutyltin bis (isooctyl thioglycolate) and dibutyltin oxide reaction products of esters of various oxygen containing acids according to the invention.

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Parts by weight Polyvinyl chloride homopolymer (Diamond 40) 100 34 at the same time maintaining at least equivalent long term resistance of the resin to major discoloration and degradation. However, where the proportion of the dibutyltin oxide-diisooctyl phthalate complex is raised to two times and five times the amount of dibutyltin lbis(isooctyl thioglycolate), it is seen that the dibutyltin oxide-diisooctyl phthalate complex actually hurts the long term stability Acrylopitre'butadiene'styrene copolymer lmpact 10 although it provides some early color improvement. mqdler (Blendex 401) O 25 Thus, it is apparent that an excessive amount of diorgano- Lubncam (Wax E) lo tin Complex is to be avoided. This amount is determined Stabilizers: by trial and error in each instance -Dibutyltin bis(isooctyl thioglycolate) EXAMPLES 25 28 (18.6% Sn) 3.0 to n Example A (containing 18.6% Sn) Oto 3.0 The following experiments were carried out in order to l demonstrate that a given ratio of diorganotin mercapto The mgredlents were first blelded and then, com' acid ester to dioranotin oxideester complex which pro- Pounded on a tworou mln Qt 350 F" f or ve mmutes vides excellent stabilization yand improved early color at heeted-0 and Cut Into smpos- The str1PS were Placed one level of total stabilizer does not necessarily profvide m an al? Ove? heated to 375 F' and samples removed the same advantage when used at much higher levels of at mmute Intervals', 20 stabilizer and, in fact, may even be poorer than the di The atachedgure 1S a bar graph of tlme ,m minutes organotin mercapto acid ester used alone at that higher (at 15 minute intervals) to yellow discoloration and to level. furlher charrmg or bsrgvlgnmg for. gash fgyzlltyl cllde Rigid or nonplasticized polyvinyl chloride resin formuresm Sample at 37 Contammg 1 u y m 1S lso' lations were prepared having the following composition: octyl thioglycolate) (from 3 to 0 parts per 100 parts 25 P h resin) and dibutyltin oxide-diisooctyl phthalate complex P l 1 h1 ,d h l afs by Wellgot (from 0 to 3 parts per 100 parts resin), each material o yVmY 1 on e OmOPO Ymef (Dlamond 4 T containing the same amount of tin (18.6% Sn). Yellow Acrylomtrll'butadlene'styfene compolymef m1* discoloration is taken to be the color of the Control A Paft modler (Blendex 401) 10 after 15 minutes of heating. Charring or browning is 30 Lubr'lfant (IWaX E) 0-25 taken to be the condition of Control A after 90 minutes Stablhzers of heating 1 NOted in 'Dahle XIII, belOW.

The cross-hatched area for each sample tested illustrates The ingredients were blended to form a homogeneous the time in minutes at 375 F. for the sample to reach mixture and the mixture was compounded on a two-roll yellow discoloration. mill at 350 F., for ve minutes, sheeted off, and cut into From this gure, it is seen that at a total concentration strips. The strips were placed in an air oven heated to 375 of 3 parts stabilizer per 100 parts resin (that is a total 0f F. and samples removed at fifteen minute intervals and at- 0.557 part tin per 100 parts resin), where the dibutyltin tached to cards. The appearance of the samples on the oxide-diisooctyl phthalate complex is employed in a ratio cards is noted in Table XIII below.

TABLE XIII l375 FJ Example Controlli Amt. Example 25 Amt. Control Y Amt. Example 26 Amt.

Db t lt' 2.0 Dibut ltin bis lsooet l 1.3 Dlbutyltln 4.0 Dibutyltin bis is oct 1 2.67 stabilizer composition bitsl (isobltyl thiogylycolate)(. y bls-(isooctyl thloglyeolate o y tliloglyco- Dibutyltin oxidefdiisooctyl 0.7 thloglyco- Dibutyltln oxlde-dlisooctyl 07 late), phthalate complex late). phthalate complex (Example A). (Example A).

Time (mins.) Color Color Color Color Initial Colorless Colorless Colorless Colorless. 15 Yellow.. Very pale yellow D0 30.- .do Pale yellow d Very pale yellow. do Light yellow-.. D0. Yellow-brown edge.-. Yellow Pale yellow. 75.- Yel1ow-brown Yellow-brown- Yellow. 90 Brown 1)?0. O. i(2) n n edges. Yellow-brown edges.

Example ControlZ Amt. Example 27 Amt. Example 2s Amt;

Stabilizer compositlon Dibutyltin bis (iso- 6.0 Dibutyltin bis (isooetyl thioglyco- 4.0 Dibutyltin bis (lsooctyl thioglyco- 5.0

octyl thioglycolate). lat late a Dibutyltin oxide-diisooctyl phtha- 2.0 Dlbutyltin oxlde-diisooctyl phtha- 1.0

late complex (Example A).

late complex (Example A).

Time (min.) Color Color Color Initial Colorless Colorless Colorless. 15 do Very pale yellow-. o. 30 Very pale yellow Pale yellow o.

d0 Light yellow.- Very pale yellow:

Yellow do to the dibutyltin bis(isooctyl thioglycolate) ranging from 0.5:2.5 to 1,511.5, that is 1:5 to 1:1, the dibutyltin oxidediisooctyl phthalate complex enhances the effectiveness of the dibutyltin bis(isooctyl thioglycolate) in lessening de- The results in Table XIII clearly show the improved effectiveness obtained `by the stabilizer combination having a ratio of 2 parts dibutyltin bis(isooctyl thioglycolate) to 1 part dibutyltin oxide-diisooctyl phthalate complex velopment of early color deterioration of the resin, while taken at two and four parts per 100 parts resin over corresponding amounts of the dibutyltin bis(isooctyl thioglycolate) alone. It is clearly seen that the complex formed from the dibutyltin oxide-diisooctyl phthalate enhances the eiectiveness of the dibutyltin bis(isooctyl thio- 36 tin oxide-tridecyl phosphite complex in improving resistance of polyvinyl chloride resin to discoloration.

Having regard to the foregoing disclosure, the following is claimed as the patentable 4and inventive embodiments glycolate) in inhibiting development of early discolora- 5 thereof: tion of the resin at these levels of total stabilizer. How- 1. A -stabilizer composition having a controlled tin conever, when 6.0 parts of stabilizer were used, the inventive tent and capable of lessening the development of early combination which was eiective at two and four parts discoloroation in polyvinyl chloride resins due to heating per hundred resin at a ratio of 2:1, no longer provided at 350 F., comprising (a) at least one organotin merthe improved early color compared to the control. capto acid ester having the formula:

However, at a ratio of 5 parts dibutyltin bis(isoocty1 Rl thioglycolate) to 1 part dibutyltin oxide-ester complex there is improvement of early color even at a level of 6 Srl-[S-Zv-(Cooiiomiz parts total stabilizer. Ri

Wilde then? 1s a fiontent 0f dlofganotm'ester complex l5 wherein R1 and IR2 are hydrocarbon radicals having from that 1S excesswe dus PTOPPUOP 1S felatd m Some Way one to about thirty carbon atoms, Z is an organic to the tgtal level of Staplhzer m he r'su?, S0 that 1t ,1S radical having from one to about thirty carbon atoms, and not possible to set .precise numerical limits on it.. This R3 is .an Organic group derived from an alcohol having appears to be peculiar to the combination of this invenfrom one to about four hydroxyl groups and from one to non' 20 thirty carbon atoms, and m is an integer from one to four, EXAMPLE 29 and (b) a diorganotin oxide complex with an ester of an Polyvinyl chloride resin compositions were stabilized OXygeIl-Contalning acid, wherein the two organo groups with combinations of dibutyltin bis(isooctyl thioglycoare eaCh attached t0 i111 through Carbon aOmS and are late), dibutyltin oxide-tridecyl phosphite complex and hydrocarbon radicals having from one to about thirty carstannous octoate according to the invention. bon atoms, and said complex is derived from the reaction Rigid or non-plasticized polyvinyl chloride resin formuof the .diorganotin oxide with an ester derived from an lations were prepared containing 100 parts of a vinyl aliphatic or aromatic alcoholl or phenol and an acid chloride homopolymer (Diamond 40). 10 parts impact selected from the group consisting of hydrocarbyl carmodiiier (Blendex 401, that is, acrylonitrile-butadieneboxylic acids, sulfur-containing hydrocarbyl carboxylic styrene copolymer). 0.25 part lubricant (Wax E) and the 30 acids, hydroxy-containing hydrocarbyl carboxylic acids, stabilizers noted -in Table XIV. phosphoric acid, sulfuric acid, sulphurous acid, nitric acid,

The ingredients were blended and compounded and nitrous acid, boric acid, arsenic acid land silicic acid. then heated on a two-roll mill at 350 F., for five minutes, 2. A stabilizer composition according to claim 1, sheeted off and cut into strips. The strips were placed wherein the diorganotin mercapto acid ester is a thioglyin an air oven, heated to 375 F. or 350 F. and samples 30 colate ester. removed at 15 minute intervals and aiixed to cards to 3. A stabilizer composition according to claim 1, show the progressive heat deterioration. The appearance wherein the organotin mercapto acid ester is a mercaptoof the samples on the cards is noted in Table XIV below. propionate ester.

TABLE Xiv (A) Example Example 9 Amt. Example 29 Aint.

Stabilizer composition Dibutyltin bis(isooctyl 1.3 Dibutyltin bis isooctyl 1.3

thioglycolate). thioglycolate) Dibutyltin oxide-tridecyl 0.7 Dlbutyltin oxide-tridecyl 0.7

phosphite complex phosphite complex (Example L). (Example L).

Stannous octoate. 0.05

Time (min.) Color Color Colorless Colorless. Very pale yellow. Very pale yellow. Pale yellow.. Do.

Yellow Pale yellow. Yellow-brown edges... Yellow. Yellow-brown Yellow-brown edges. Brown Yellow-brown.

TABLE XIV (B) Example Example 9 Amt. Example 29 Amt.

Stabilizer composition Dibutyltin bis(isoocty1 1. 3 Dibutyltin bis(isooctyl 1. 3

thioglycolate). thioglycolat Dibutyltiri oxide-trideeyl 0.7 Dibutyltin oxide-tridecyl 0.7

phosphite complex phosphite complex (Example L). (Example L).

Stanrious octoate. 0. 05

Time (min.) Color Color Initial Colorless Colorless. i5 dem Do.

Do D

Do. Pale yellow. 120 .do Light yellow.

The results in Table XIV clearly indicate that the stannous octoate enhanced the eifectiveriess of the combina- 4. A stabilizer composition in accordance with claim 1, wherein the diorgano-tin mercapto acid ester is a dialkyltion of dibutyltin bis(isooctyl thioglycolate) and dibutyltin mercapto acid ester.

S. A stabilizer composition in accordance with claim 4, wherein the dialkyl portion is dibutyl.

6. A stabilizer composition in accordance with claim 4, wherein the dialkyl portion is dioctyl.

7. A stabilizer composition in accordance with claim 1, wherein the diorganotin oxide is dibutyltin oxide.

8. A stabilizer composition in accordance with claim 1, wherein the diorganotin oxide is a dioctyltin oxide.

9. A stabilizer composition according to claim 1, wherein the organotin mercapto acid ester is a dibutyltin mercapto acid ester and the diorganotin oxide-ester complex is a dibutyltin oxide-ester of an oxygen containing acid complex.

10. A homogeneous liquid stabilizer composition according to claim 1, wherein the organotin mercapto acid ester is dibutyltin thioglycolate ester and the diorganotin oxide-ester complex is a dibutyltin oxide-ester complex.

11. A homogeneous liquid stabilizer composition according to claim 1, wherein the organotin mercapto acid ester is dioctyltin thioglycolate ester and the diorganotin oxide-ester complex is a dioctyltin oxide-ester complex.

12. A stabilizer composition in accordance with claim 1, wherein the organotin mercapto acid ester is dibutyltin bis (isooctyl thioglycolate) and the diorganotin oxide-ester complex is a dibutyltin oxide-ester complex.

13. A stabilizer composition in accordance with claim 1, wherein the organotin mercapto acid ester is a dibutyltin mercaptopropionate ester and the organotin oxide-ester complex is a dibutyltin oxide-ester complex.

14. A stabilizer composition according to claim 1, wherein the molar ratio of the tin present in the organotin oxideester complex to the tin present in the diorganotin mercapto acid ester is within the range from about 0.25 :l to about 1:1.

15. A stabilizer composition in accordance with claim 1, wherein the tin present in the combination of the organotin mercapto acid ester and the diorganotin oxide-ester comprises from about 5 to about 45% 16. A stabilizer composition in accordance with claim 1, wherein the tin present in the combination of the organotin mercapto acid ester and the diorganotin oxideester comprises from about l0 to about 30%.

17. A stabilizer composition according to claim 1, wherein the diorganotin oxide-ester complex is a reaction product of diorganotin oxide and an ester selected from the group consisting of hydrocarbyl carboxylic acid esters, hydrocarbyl thiodicarboxylic acid esters and phosphorus esters.

18. A stabilizer combination in accordance with claim 1, including, in addition, a divalent stannous tin salt, con- 38 taining two groups selected from the group consisting of bromide, chloride, and organic groups which are the residue of non-nitrogenous organic compounds having an active hydrogen which is attached to oxygen or sulfur and which is replaceable by a metal.

19. A polyvinyl chloride resin composition having an enhanced resistance to early discoloration when heated at 350 F. comprising a polyvinyl chloride resin `and a stabilizer composition in accordance with claim 1.

20. A polyvinyl chloride resin composition in yaccordance with claim 19, including, in addition, a divalent stannous tin salt, containing two groups selected from the group consisting of bromide, chloride, and organic groups which are the residue of non-nitrogenous organic compounds having an active hydrogen which is attached to oxygen or sulfur and which is replaceable by a metal.

21. A polyvinyl chloride resin composition according to claim 19, wherein the organotin mercapto acid ester is a dialkyl tin thioglycolate ester.

22. A polyvinyl chloride resin composition according to claim 19, wherein the organotin acid ester is a dialkyltin mercaptopropionate ester 23. A polyvinyl chloride resin composition according to claim 19, wherein the stabilizer composition is present in an amount within the range from about 0.25 to about 10% by weight of the resin.

24. A polyvinyl chloride resin composiiton according to claim 23, wherein the tin present in the stabilizer composition comprises from about 5 to about 45% by weight of the stabilizer composition.

References Cited UNITED STATES PATENTS 2,597,920 5/ 1952 Caldwell 26045.75 2,598,496 5/ 1952 Bradley 260-45.75 2,626,954 l/ 1953 Albert 260-45.75 2,629,700 2/ 1953 Caldwell 260-45.75 2,648,650 8/ 1953 Weinberg 260-45.75 2,763,632 9/ 1956 Johnson 260--45.75 2,914,506 11/ 1959 lMack 260--45.75

DONALD E. CZAJA, Primary Examiner V. P. HOKE, Assistant Examiner U.S. Cl. X.R. 

